Device for the recording or reproduction of sound tracks



Aug. 28, 1962 E. K. KNUDsEN DEVICE FOR THE RECORDING OR REPRDUCTION OF'SOUND TRACKS Filed MaI'Gh 2. 1959 2 Sheets-Sheet 1 Illini Aug. 2s, 1962E. K. KNUDSEN 3,051,798

DEVICE FOR THE RECORDING OR REPRODUCTION OF SOUND TRACKS Filed March 2,1959 2 Sheets-Sheet 2 United States Patent O mark Filed Mar. 2, 1959,Ser. No. 796,655 Claims priority, application Denmark Mar. 5, 1958 3Claims. (Cl. 179-100.41)

The present invention relates to an electromechanical recording andreproducing head of the type having two movable electromechanicalmembers connected to a mechanical oscillating system, comprising `anarmature and la needle responsive to both vertical and lateralmodulation.

The operating principles of devices of this class, for uses such yasdisc recording, are known. As a practical matter, however, the crossmodulation produced by the mechanical interaction of the twoelectromechanical members through the armature has preventedsatisfactory results from being obtained. Previous attempts to reducethis cross modulation have proceeded on the basis that the masses of theelectromechanical members must be increased while the mass of theoscillating system must he reduced.

The results of these attempts have not been acceptable since theattendant increase in the dimensions `and weight of the apparatus,together with the loss of mechanical rigidity of the armature, whichlimits the high frequency response of the head, have rendered thesesolutions to the problem both impractical and unsatisfactoryAccordingly, it is an object of this invention to provide anelectromechanical head structure which is not subject to theaforementioned problems and limitations.

Another object of the invention is to provide a recording andreproducing head which possesses a substantially uniform frequencyresponse throughout the usable frequency spectrum.

A further object of the invention is to provide a head structure capableof response to both vertical and lateral modulation characteristics andwhich is substantially free from any cross modulation effects.

A still further object of the invention is to provide a head structurecapable of recording or reproducing two channels with a single needle.

Y According to a preferred embodiment of the invention, an elongatedarmature with a needle mounted centrally thereon has anelectromechanical member connected to the armature symmetrically on eachside of the needle, the distance between each of the points of action ofthe two electromechanical members on the armature and the centre ofgravity of said oscillating system being equal to where I is the momentof inertia of the oscillating system about an axis through the centre ofgravity of said oscillating system perpendicular to the plane formed bythe points of the needle and said two points of action of theelectromechanical members on the armature, While M is the mass of theoscillating system. Energizing either or both of the electromechanicalmembers produces mechanical oscillation of the yarmature which in turncauses the needle to be oscillated either vertically or laterally, or inboth directions simultaneously.

In a preferred embodiment of the invention said centre of gravity islocated substantially on a straight line through said two points ofaction.

Preferably a mechanical rigid elongated armature is used connected totwo coils forming the two movable electromechanical members. It can thusbe seen that 3,051,798 Patented Aug. 28, 1962 lCC this structure impliessome increase in the mass of the armature beyond the minimumrequirements for mechanical rigidity. On the other hand, however, thecoil structures, which are considerably heavier than the armature, maybe made `as light as possible, thereby enabling an overall reduction inmassi.

This preferred embodiment of the invention is illustrated in theaccompanying dnawings in which:

FIG. 1 is a front view of `a part of a device according to theinvention;

FIG. Z is an oscillating system under the action of the twoelectromechanical members operating in in-phase relation;

FIG. 3 is the oscillating system under the action of the twoelectromechanical members operating in counter phase relation;

FIG. 4 is the oscillating system under the action of one of the twoelectromechanical members only, and

FIGS. 5, 6 and 7 illustrate various types of track recording undervarious combined actions of the electromechanical members.

In FIG. 1 a device is shown comprising two electromechanical members inthe form of oscillating coils 1 and 2 having parallel directions ofmotion. Each of the oscillating coils is connected to an armature 3 atpoints of action 4 and 5, respectively. The yarmature 3 has a needle 6,the point of which is so located that the lines connecting the point ofthe needle 6 with each of the two points of action 4 and 5 form an angleof 90. The coils 1 and 2 are supported conventionally in housing 9 byAmeans of leaf springs .10 and 11 which are arranged radially inrelation to the 'axis of the coils.

The armature 3 has a center of gravity 7 located on or near `a straightline through the two points of action 4 and 5, and the armature issymmetrically constructed so that the .two points of `action 4 and 5 arelocated at the same distance x from the center of gravity on each sidethereof.

FIG. 2 shows how such a device will cut into a record when the twooscillating coils 1 and 2. are operating in in-phase relation. Thearmature then move vertically up and down, and in `a record 8 =a trackwill be cut with vertical or hill-and-dale modulation as indicated bydotted lines.

If the two oscillating coils 1 and 2 are operating in counter phaserelation, the armature 3 will be moved as shown in FIG. 3. In view ofthe very small movements, the curvature of the paths of motion may beneglected and the point of needle 6 `will therefore make a transversemovement only as shown by dotted lines, a transverse modulation beingthereby eifected.

FIG. 4 illustrates how the armature will move, if only one of theoscillating coils is operating. Provided that the above-stated conditionis fulilled, an action of the oscillating coil 2 at the point of Vaction5 cause the `armature to pivot about the point of action 4, and thepoint of the needle 6 will therefore perform a movement which may beconsidered rectilinear in a direction forming an angle of 45 with thehorizontal plane. Thereby a sound track as shown in FIG. 5 will berecorded, and it appears from FIG. 6 how the corresponding recording ofa sound track will be effected when the oscillating coil 1 is operatingalone.

The combined movements will appear from FIG. 7 Where, -two independentmodulations may be recorded in a two-channel system for instance, forstereophonic reproduction.

It will be seen from FIG. 2. that by hill-.and-dale movement each of theltwo oscillating coils will be loaded by half of the the armature, i.e.by M/Z. When the needle is moving transversely as shown in FIG. 3, andif the armature is so designed that the load become i.e. the same loadas for hill-and-dale movement.

In FIG, 4 the armature is operated by one of the oscillating coils only.Still provided the armature will pivot about the point of action of theother coil, and no power wll'l be transferred thereto.

A one-sided action 'of a force P `at the point of action will, accordingto the laws of physics, impart a movement to the armature composed oftwo components, i.e. a translatory movement in the direction of. theforce P thereby setting up a resistance of inerti-a equal to an oppositethe direction of Ithe force P, and, owing to the fact that theresistance of inertia will act in the center of gravity 7, a rotation ofthe larmature about the center of gravity set up by the torque P-x. Thepoint S will therefore have two accelerations i.e.

O51=I I owing to the tr-anslatory movement, andv 1 -P P a2 1 Ma M owingto the rotation, the effective mass in the point 5 during pivoting aboutthe center of gravity being equal to the moment of inertia divided byx2. It will be seen that when the armature is designed according to theinvention, the two components of acceleration will have the same size,and the resulting 'acceleration in the point 5 will therefore be 4x2 I4x2 2 because the moment of inertia `of the oscillating system byrotation about the point 4 is I -l-Mx2. It will be understood that theload of masses be the same for all the types of motion mentioned, andcross modulation is avoided by the fact .that one of the oscillatingcoils only set up a pure rotation or 'pivoting ofthe osv 4 cillatingsystem about the point of action of the other coil on the armature.

While the invention has been illustrated and described in oneembodiment, it is recognized that variations and changes may be madetherein without departing from the invention yas set forth in theclaims.

vHaving described my invention, I claim:

1. In an electromechanical recording and reproducing device, amechanical oscillating system comprising an elongated iarmature.including a needle mounted centrally thereon, a plurality ofelectromechanical members connected to the armature symmetrically oneach side of said needle, the connection between each of theelectromechanical members and the armature being so arranged that thelarmature is carried by said electromechanical members and that twofixed and sharp points of action are defined through which no turningmoment may be transmitted, the armature being fur-ther provided withextensions extending outwardly from said points of action, saidextensions being so arranged that the center of gravity of the armatureis l'positioned substantially on a straight line` through the two pointsof action so that the distance between each of the two points of actionand said center of gravity is equal to where I is the moment of inertiaof the armature about an axis through said center of gravityperpendicular to the plane formed by the point of the needle and saidtwo points of action, while M is the mass of the armature.

v2. In Ia device of the class described, a mechanical oscillating systemcomprising a mechanical rigid elongated armature with `a needle mountedon said armature at the center of gravity thereof, a coil connected tothe armature symmetrical on each side of the center of gravity dening iapoint of action therefor, the distance between each of the points ofaction of the two coils on the armature and the center of gnavity ofsaid oscillating system being equal to where I is the moment of inertiaofthe Aoscillating system about an axis through thel centre of gravityof said oscillating system perpendicular to the plane formed by thepoints of the needle and said two points of action of the coils on thearmature, while M the mass vof the oscillating system. v

3. In a deviceof the class described, and according to claim 2, whereinsaid center of gravity is located sub stantially on a straight linethrough said two points of action.

References Cited in the le of this patent v UNITED STATES PATENTS2,025,388 Henning Dec. 24, 1935 2,027,168 Harrison Jan. 7, 19362,093,540 B1um1ein sept. a1, 1937 2,864,897 Kaar Dec. 16, 1958 FOREIGNPATENTS 688,804 Great Britain Mar. l1., 1'953

